The tendency for wheel trucks on railway cars to move from side to side while traveling on straight track is called "truck hunting" and has long been known to place such stress on the wheel tread and flanges as to cause accelerated failure to wheels and also to truck components along with damage to track structure. This causes higher maintainance costs and also extreme costs when derailments occur as a result of "truck hunting".
In 1893 a patent was issued on the use of pendulums to resist this movement, so as to attempt to hold the axle of the wheel-truck at a right angle to the line of draft during straight track travel. However, the pendulums would also cause such resistance at the time the wheels came to a curve section as to put excessive strain on the wheels during the curve section travel.
As the years went by coil spring systems were used for the same purpose as the pendulums and then later leaf springs were proposed in a patent issuing in 1925. But the leaf and coil springs had the same disadvantage as the pendulums, namely, they placed undue stress and wear on the wheels as the wheels rounded the curves.
There was even a problem that the more the curve, the more the stress because the pendulums would be farther from vertical thus exerting greater force or the springs would be farther from normal position and exerting greater force. As a result wheels could fail from the stress applied on them at the curve, even though the springs could provide help in relieving stress on the straight track section.
By 1938 it was recognized that a releasing of pressure was desirable so that the wheel-trucks could turn freely on a curved track section, but the proposal for accomplishing this utilized springs and cam surfaces. Cam surfaces, however, cannot provide a sudden and an abrupt and an immediately operative freeing of a stabilizer.
Since 1938 many proposals have been made for the multiplying of forces by hydraulics so that a spring in a check valve can be used as the force to restrain a truck.
My basic concept in its referred embodiment involves the use of a hydraulic cylinder assembly having an openable by-pass passageway, the assembly being mounted with its ends directly, or indirectly, connected to the car body and truck respectively. The length of the cylinder assembly is hydraulically locked so as to prevent oscillation of the truck during straight track travel, by having the by-pass passageway blocked, by the piston or by another type of blocking member such as a moving valve member, during straight track travel, the passageway becoming opened at a time when the truck has reached a curve because of the position that the piston or other blocking member is placed in by the wheel-truck when the wheel-truck is rotated by the curved track.
This uncovering of the passageway makes possible the release of the hydraulic locking, the release being abrupt and full so that the wheel-truck can then take the curve freely without the oscillation resistance system of this invention interferring with swiveling of the wheel-truck.
With my concept there would be no pressure forcing the wheels against the rails during curved track travel, thereby eliminating and wear and stress on the wheels which would otherwise occur if my releasing feature is not used.
My concept further involves the advantage that when the wheel-truck reaches a straight track section again, then the piston will have been caused to reach a position in the cylinder housing for covering up and closing off the passage way means again, so that the hydraulic pressure for controlling oscillation is once more in effect.
In some applications, the automatically releasing stabilizer of my invention may be advantageously combined with a cam surface in order to further increase control over truck position during straight track travel. The cam surface used in this application is contoured to cause wheel truck rotation encountered during straight track travel to induce greater piston travel than wheel truck rotation encountered during curved track travel.
A position I prefer for the check valves, is in the piston itself, there being two check valves, one to stop flow in each direction of truck motion during oscillation.
A further object of this invention is to provide in the combination a feature of hydraulic engineering used some in other fields, but not used in anti-hunting devices to my knowledge.
This feature is means for compensating for the fact that in a simple hydraulic cylinder the piston rod is ordinarily reducing the volume in the housing on one side of the piston; whereas, ordinarily, there is no piston rod on the other side of the piston to provide a balancing reduction of the amount of fluid occupying the housing portion on the other side of the piston. This compensation can be accomplished in various ways. One such way is the use of a bellows or flexible sealing device.
When cars are run empty or with light load, this truck hunting may become a very serious problem. Experiments and data taken on many truck hunting tests have developed that trucks on empty cars may start hunting at speeds less than 40 MPH. Other cars can run at higher speed, but it appears that many cars begin to have serious problems with truck hunting when speeds exceed 55 to 60 MPH. Some can reach 70 to 80 MPH with no serious problem, but hunting of a lesser degree is still prevalent.
Loaded cars tend to be less susceptible to truck hunting due to higher friction force at the truck center plate and casting. When this frictional force exceeds the force of the rail to wheel adhesion, the truck tends to stay centered and steer down the rail.
Numerous tests have been made throughout the past several years, and it has been determined that a significant amount of hunting occurs at a side to side or rotational frequency of approximately 3 cycles per second.
The frequency depends upon many variables. However, any hunting in this frequency range is detrimental to equipment from a wear and fatigue standpoint.
Excessive wheel flange and tread wear, wear on truck pedestal liners, bolster gibs, bearing adapters, and brake suspensions and also center casting wear may be accelerated by truck hunting.
Along with this, the car body is flexed and twisted with each hunting cycle, which may cause accelerated fatigue fractures in side sheets.
Of prime importance is the danger of derailment when truck hunting is accompanied by rock and roll and the wheel lifts over the rail--which has been suspect in many derailments.
Many railroads have placed speed restrictions on certain cars because of truck hunting which has been thought to create derailment problems. This may cause a serious problem in over-all railroad operation and train and car scheduling, making it necessary to restrict train speed on many trains.
The industry is quite aware of these problems and has expended large sums of money in testing, designing and retesting schemes which include new design trucks, and numerous frictional side bearing arrangements to add frictional forces to the center casting or change the suspension to allow wheel movement without truck movements. Several new trucks have been designed and tested. Some have had a marginal degree of success which appears to parallel the amount of money the suppliers or industry want to spend for these fixes.
The system proposed in this invention is to retard the truck rotational movement in a limited arc, then allow free truck movement thereafter in order to afford free movement to negotiate curves, turn-outs, and cross-overs. Truck hunting is attenuated through curves due to reduced speeds for curve restrictions and because centrifugal forces tend to hold the wheel flanges against the rail through the curve.
In the prior art many patents utilized heavy springs to damp ascillation as described, I do use a spring for the purpose of causing the piston to return to a normal position for straight track travel, but such a spring need not be heavy since the main work of damping the truck oscillation is being done through the hydraulic system of this invention.
A special objective of this invention is to provide the concept of using a roller and a roller receiving notch assembly with the roller mounted either on the truck or on the car body, and with the notch mounted on the other of the truck or car body and with the roller held in place, either by a piston rod, or by a lever connected to a piston rod of a hydraulic anti-hunting assembly, the roller and notch system providing a means of making a single acting hydraulic cylinder to damp or lock the pivoting of the truck in either direction with the roller being permitted to climb out of the notch as the truck turns either clockwise or counterclockwise.
An object of the invention is to provide a hydraulic stabilizer system, using a hydraulic cylinder with a restricted motion control port capable of resisting hunting, yet permitting lesser oscillations of the harmless sort, and for permitting a wheel-truck to round very gradual curves without substantial resistance. That is curves which are so gradual that they would not move the piston into a position for releasing fluid into a by-pass line extending from a portion of the cylinder wall, which is on one end thereof and, therefore, one one side of the piston, to a portion of the cylinder wall which is on the other end thereof, and, therefore, on the other side of the piston. I call such a stabilizer a single acting stabilizer with motion control port. Such a stabilizer can work effectively with the roller and notch system above described, provided its piston has a return flow check valve, permitting fluid to flow back to the right side of the piston when the return spring is moving the roller back into its notch.
Another object of the invention is to provide a double acting cylinder wheel-truck stabilizer, the ends of which are attached directly to the wheel truck and the car body, and the piston of which is provided with pressure check valves permitting flow therethrough from left to right and right to left, respectively, but only when the wheel-truck has reached a curve. This is because the springs of the check valves are intentionally sufficiently strong as to substantially prevent oscillation of the wheel-truck.
A further object is to provide the concept of a velocity sensitive valve stabilizer, the piston of which has a velocity sensitive valve mounted therein permitting flow around the valve freely, so long as the flow is slow, but when the flow reaches a higher velocity, such as the velocities that result from truck hunting, the valve will close for preventing truck hunting.
A further object of the invention is to provide a single acting stabilizer with squeeze frame, which comprises a hydraulic cylinder with a piston having a pressure check valve in it of sufficient strength as to resist truck hunting and yet being overcomable for permitting the rounding of curves, the piston having a return flow check valve in it, and the piston being urged into normal position by a compression spring, the frame of the stabilizer of this modification having a truck mounted part and a body mounted part mounted in positions such that when the truck attempts to turn about is vertical axis in one direction, the cylinder assembly will be squeezed or placed under compression. Two stabilizers of this modification are used, one on the left and one of the right side of the wheel-truck for taking care of clockwise and counter-clockwise pivoting, respectively.
Still another object of this invention is to provide a box type stabilizer modification in which a hydraulic cylinder is nested between the upper and lower halves of a box frame, the top part of a box frame being fixed to the underside of a railway car, and the underside of a box frame is attached to the wheel-truck. The box frame sections move with respect to each other in one direction as the wheel-truck pivots clockwise, and in another direction as the wheel-truck pivots counter-clockwise, and in either of these wheel truck movements the hydraulic cylinder of this modification is under compression forces. The piston in this modification is provided with a pressure check valve overcomable only during wheel-truck rounding of a section of curve track, but capable of resisting truck hunting oscillations, the piston having a return flow valve, permitting flow therethrough. When the truck enters a curve with this modification, the flow passing through the piston pressure check valve is accommodated by a diaphragm for keeping the fluid between the diaphragm and the piston, a spring returning the parts of this hydraulic cylinder modification to original position, and a by-pass passage in this modification coming open only when compression of the hydraulic cylinder assembly is sufficient as to be proportional to the need for the truck to round a curve in the track which it then does without resistance, because of free flow through the by-pass passage.
Still another object is to provide a vertically moving stabilizer modification in which a hydraulic cylinder assembly and return spring are mounted to cooperate with a vertically moving roller which is received normally in a notch of an element mounted either on the wheel-truck or railway car with the hydraulic cylinder and roller being mounted on the opposite one of the wheel-truck and railway car, with the hydraulic cylinder preferably mounted in the truck. A single acting hydraulic cylinder is sufficient for this use and can have a truck motion control port extending through the piston, permitting harmless oscillations below the damaging truck hunting frequencies, the piston having a return flow valve, and the cylinder having by-pass passage means, which can be grooves in a wall thereof, positioned to release fluid for free flow from one side of the piston to the other at times when the piston has moved from normal straight track travel position sufficiently to indicate that the truck is beginning to round a curve, so that the roller must come completely out of its notch.
Still another modification of the invention is the camleaf-spring modification, which provides a stabilizer utilizing a lever pivoting on a railway car mounted fulcrum, and having a roller at one end normally received in a notch in a radius element attached to the wheel-truck, the other end of the lever having a spring engaging roller engageable with the leaf spring fixed to the railway car. The leaf spring having an offset portion adapted to receive the spring engaging roller, the offset portion being farther from the fulcrum of the lever so that when a truck enters a curve the roller can climb out of its notch with greater ease because the spring engaging roller can pass over on to the offset portion of the leaf spring, whereby lesser pressure is applied by the spring for holding the notch roller in place. When the wheel-truck again comes to a straight track section out of a curved track section the spring engaging roller will climb a gradually inclined surface on the spring back on to a main part of the spring, so that the spring applies pressure for holding the notch roller in its notch to resist wheel-truck oscillation during straight track travel, with sufficient force as to substantially prevent all truck hunting oscillations of the equipment damaging type.
It is common for railroad tracks to have gradually increasing curvature along a substantial length of track as the track extends from a straight track section toward a curved track section. This is somewhat different from many automobile super highways in which the curvature is on a radius immediately as it leaves the straight track section.
When the only way of releasing the hydraulic pressure in a wheel-truck stabilizer is by a prior art method of a by-pass line from one end of the cylinder to the other, which passes through a pressure check valve, then the spring of that valve will cause a hydraulically multiplied force, resisting the increasing degrees of turning of the wheel-truck, wearing away the flanges of the wheel-truck against the rails.
The hydraulic stabilizers of this invention can be adjusted, for example, to resist only amounts of wheel-truck turning which are the equivalent of a one and a half degree rail curvature, so as to prevent hunting. Many rail curvatures extend as high as fifteen and even twenty degrees, with approximately eight degrees being the average curve in the United States, as a guess, in my opinion. Therefore, since most rail curves in the United States are in excess of a one and a half degree curvature the hydraulic stabilizers of this invention will reduce stabilizer-caused wheel flange wear and rail wear along the vast majority of the degrees of curvature traveled by the many railroad cars in the country.